[RFC-PATCH] nfsd: when unhashing openowners, increment openowner's refcount

[Alex Lyakas <alex@zadara.com>]

release_openowner() expects an extra refcnt taken for the openowner,
which it is releasing.

 With nfsd_inject_forget_client_openowners() and nfsd_inject_forget_openowners(),
we unhash openowners and collect them into a reaplist. Later we call
nfsd_reap_openowners(), which calls release_openowner(), which releases all openowner's stateids.
Each OPEN stateid holds a refcnt on the openowner. Therefore, after releasing
the last OPEN stateid via its sc_free function, which is nfs4_free_ol_stateid,
nfs4_put_stateowner() will be called, which will realize its the last
refcnt for the openowner. As a result, openowner will be freed.
But later, release_openowner() will go ahead and call release_last_closed_stateid()
and nfs4_put_stateowner() on the same openowner which was just released.
This corrupts memory and causes random crashes.

After we fixed this, we confirmed that the openowner is not freed
prematurely. It is freed by release_openowner() final call
to nfs4_put_stateowner().

However, we still get (other) random crashes and memory corruptions
when nfsd_inject_forget_client_openowners() and
nfsd_inject_forget_openowners().
According to our analysis, we don't see any other refcount issues.
Can anybody from the community review these flows for other potentials issues?

Signed-off-by: Alex Lyakas <alex@zadara.com>
---
 fs/nfsd/nfs4state.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 7857942..4e9afca 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -7251,6 +7251,7 @@ static u64 nfsd_foreach_client_lock(struct nfs4_client *clp, u64 max,
 			func(oop);
 			if (collect) {
 				atomic_inc(&clp->cl_rpc_users);
+				nfs4_get_stateowner(&oop->oo_owner);
 				list_add(&oop->oo_perclient, collect);
 			}
 		}
-- 
1.9.1